sirji -sir- gismu

x1 is straight/direct/line segment/interval between x2 and x3; (adjective:) x1 is linear.

See also korcu, linji, kruvi, kuspe.

In notes:

korcu
(adjective:) x1 is bent/crooked/not straight or direct/[twisted]/folded.
kruvi
x1 is a curve/turn/bend in x2, at locus x3, and defined by set of points/properties x4.
kuspe
x1 ranges/extends/spans/persists/reaches across/over interval/gap/area/scope/extent/range x2.
linji
x1 is a line/among lines [1-dimensional shape/form] defined by set of points x2.